Home Office officials planned to worsen the health of an Iraqi asylum seeker who had a mental illness in the hope of putting pressure on him to leave the UK, the high court has heard.

The case centres on evidence that appears to show that they tried to exert pressure on the man, who is seriously ill with paranoid schizophrenia, to sign a form agreeing to return voluntarily to his home country.

Officials from the UK Border Agency are unable to force failed asylum seekers to return to Iraq against their will because the country is considered to be too dangerous. In 2009 when this arose, they were keen to encourage voluntary returns, however.

The man, who can be referred to only as A as a court order protects his identity, was suffering from a series of fixed delusional beliefs and lacked the capacity to make informed decisions, according to medical records read out in court.

Because of this vulnerability he is being represented in the high court case by the official solicitor.

A's legal team argue that he was held unlawfully in immigration detention for periods between 2007-2010. UKBA's legal team deny the detention was unlawful.

UKBA records disclosed to the court reveal a damning insight into how far officials may have been prepared to go to get the man to leave the UK.

He was serving a jail sentence at HMP Manchester for threatening someone with a screwdriver while suffering from paranoid delusions.

Documents appear to show that officials wrote in their notes in 2009 that he was getting "too comfortable" in the prison and that a new environment may persuade him to return to Iraq voluntarily.

One official wrote: "I propose that he be moved to an immigration removal centre to unbalance him".

The statement appears to acknowledge what many campaigners against immigration detention claim – that detention can damage the mental health of detainees.

Amanda Weston, acting for A, told the court: "The proposal to move him with the objective to cause him to be unbalanced and to put pressure on him to consent to voluntary removal was improper."

UKBA emails disclosed to the court also reveal that pressure was applied to a nurse to persuade him to sign a form agreeing to go back to Iraq.

David Hervey, the assistant director of UKBA's criminal casework directorate, wrote to a colleague, Denise Burgis: "I asked you to speak to his mental health nurse to enlist her help in explaining the FRS (voluntary return) process … The whole point of asking her to do this rather than the immigration officer is that he seems to trust Leena Spencer."

Spencer responded by saying: "Denise has asked whether I can attempt to explain the deportation process to A again in an attempt to ensure that he signs the relevant paperwork. I have reiterated that I am a nurse not an immigration worker and that Mr Platt (an immigration officer) has given all the information to A but he refuses to sign any forms."

A psychiatrist who has previously worked in immigration detention centres expressed concern about the revelations. He asked not to be named.

"I'm not surprised to hear about this though. It is totally normal in immigration detention. UKBA do not show any respect for the psychiatric profession. They have failed to understand the effect of his mental illness on his ability to make decisions."

Emma Ginn, the co-ordinator of Medical Justice, condemned UKBA for its treatment of the man.

"UKBA have a duty of care to vulnerable detainees. The disclosure that they planned to 'unbalance' the mind of a man already suffering from schizophrenia is a profoundly disturbing insight into what goes on behind closed doors."

A UKBA spokesman said that no comment would be made until after the conclusion of the case. Judgment is expected to be reserved.